This database includes 25 long-term ECG recordings of human subjects with
atrial fibrillation (mostly paroxysmal). Of these, 23 records include the
two ECG signals (in the .dat files); records 00735 and 03665 are
represented only by the rhythm (.atr) and unaudited beat
(.qrs annotation files.

The individual recordings are each 10 hours in duration, and contain
two ECG signals each sampled at 250 samples per second with 12-bit
resolution over a range of ±10 millivolts. The original analog
recordings were made at Boston's Beth Israel Hospital (now the Beth
Israel Deaconess Medical Center) using ambulatory ECG recorders with a
typical recording bandwidth of approximately 0.1 Hz to 40 Hz. The
rhythm annotation files (with the suffix .atr) were prepared
manually; these contain rhythm annotations of types (AFIB
(atrial fibrillation), (AFL (atrial flutter), (J (AV
junctional rhythm), and (N
(used to indicate all other rhythms). (The original rhythm annotation
files, still available in the old directory,
used AF, AFL, J, and N to mark these
rhythms; the atr annotations in this directory have been
revised for consistency with those used for the MIT-BIH
Arrhythmia Database.) Beat annotation files (with the
suffix .qrs) were prepared using an automated detector and
have not been corrected manually. For some records, manually
corrected beat annotation files (with the suffix .qrsc) are
available. (The .qrs annotations may be useful for studies
of methods for automated AF detection, where such methods must be
robust with respect to typical QRS detection errors. The
.qrsc annotations may be preferred for basic studies of AF
itself, where QRS detection errors would be confounding.) Note that
in both .qrs and .qrsc files, no distinction is made
among beat types (all beats are labelled as if normal).

Until November 2000, only one of the signal files (for record 04936) was
available. The original 9-track tapes from 1983 for these records have
now been read to produce the other signal files in this directory. In
a few cases (04043, 08405, and 08434) isolated data blocks from the original
tapes were unreadable. In these cases, the missing data, corresponding to
10.24 seconds for each missing block, have been replaced with a flat segment
of samples with amplitudes of zero. See notes.txt
for details.

In March 2014, Henian Xia reported that the .qrs annotations were
not aligned with the ECG waveforms in record 07859, and investigation showed
that 2569 samples appeared to be missing from the beginning of the record.
The original annotation file has been renamed 07859.qrs-, and a
realigned version of it (without its initial 14 annotations) is available as
07859.qrs. A correctly aligned, manually reviewed annotation
file was also produced at that time, and is now available here
as 07859.qrsc.